Acromyrmex volcanus Wheeler 1937

Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia

Range

Costa Rica, Nicaragua.

Identification

Median pronotal spines usually absent, occasionally present as low tubercles, never distinct spines; head not tapering behind eyes; head width less than or equal to 3.2mm; propodeal spines smoothly or irregularly conical, not carinate; dorsal face of propodeum with pair of indistinct blunt setose tubercles anterior to spines; smaller workers red to yellow-brown, major workers dark brown to black; head width less than or equal to 3.2mm.

Natural History

Acromyrmex volcanus is common in mature wet forest on the Atlantic slope of Costa Rica, occurring from sea level to about 1000m elevation. It is one of the most common and conspicuous attines in lowland primary forest, giving way to Atta in second growth and more open habitats.

At La Selva Biological Station, A. volcanus workers forage on the ground but nests are arboreal. When I first encountered the species in 1985, I was mystified by the large workers cutting fallen flowers on the forest floor and carrying them up tree trunks. Later, while climbing a tall Pentaclethra tree at La Selva, I was standing in the first major fork, 20m above the forest floor, when Acromyrmex workers suddenly appeared around my feet. I found a basketball-sized nest, with a large fungus garden, embedded in the accumulated canopy soil beneath the epiphyte layer in the fork. Subsequent observations by Wetterer and others have repeatedly confirmed the arboreal nesting habits at La Selva, but at elevations above 500m A. volcanus nests at ground level (Wetterer, pers. comm.). Wetterer (1993) reports quantitative data on the foraging and nesting ecology of A. volcanus at La Selva.